1. Field of the Invention
The present invention relates generally to variable compression ratio internal combustion engines. More particularly, the invention relates to a variable compression ratio engine having a variable compression apparatus operable using a field-sensitive fluid.
2. Background Art
The xe2x80x9ccompression ratioxe2x80x9d of an internal combustion engine is defined as the ratio of the cylinder volume of when the piston is at bottom-dead-center (BDC) to the cylinder volume when the piston is at top-dead-center (TDC). The higher the compression ratio, the higher the thermal efficiency of the internal combustion engine. This in turn results in improved fuel economy and a higher ratio of output energy versus input energy of the internal combustion engine.
In conventional internal combustion engines, however, the compression ratio is fixed and thus the engine efficiency cannot be optimized during certain operating conditions to improve fuel economy and engine power performance. Accordingly, so-called xe2x80x9cvariable compression ratioxe2x80x9d (VCR) internal combustion engines have been developed having, for example, higher compression ratios during low load conditions and lower compression ratios during high load conditions. Conventional techniques for varying compression ratio include using xe2x80x9csub-chambersxe2x80x9d and xe2x80x9csub-pistonsxe2x80x9d to vary the cylinder volume, see for example U.S. Pat. Nos. 4,246,873 and 4,286,552; varying the actual dimensions of all or a portion of a piston attached to a fixed length connecting rod, see U.S. Pat. No. 5,865,092; and varying the actual length of the connecting rod itself, see U.S. Pat. Nos. 5,724,863 and 5,146,879.
Many conventional techniques however rely on the use of complex and costly hydraulic control systems for varying the length of a connecting rod or height of a reciprocating piston. In U.S. Pat. Nos. 5,562,068, for example, a hydraulic system is used to vary the effective length of a connecting rod by rotating and selectively locking an eccentric ring located within the large end of the rod. When hydraulic pressure is released, the eccentric ring interlocks with the crank pin thus resulting in a longer effective rod length and therefore a higher compression ratio mode. When hydraulic pressure is applied, the eccentric ring locks with the connecting rod, thus resulting in a shorter effective rod length and therefore a lower compression ratio.
U.S. Pat. No. 5,960,750 similarly discloses a connecting rod having a rotatable eccentric ring actuated by a hydraulic control system. The connecting rod includes a mechanically actuated locking member for locking the eccentric ring in one of two positions. When actuated in a first direction, the locking member locks the eccentric ring in a position corresponding to a maximum effective length of the connecting rod, i.e., a high compression ratio mode. When actuated in a second direction, the locking member locks the eccentric ring in a position corresponding to a minimum effective length of the connecting rod, i.e., a high compression ratio mode.
U.S. Pat. No. 5,417,185 and Japanese Publication JP-03092552, which disclose rings disposed between the xe2x80x9csmallxe2x80x9d end of a connecting rod and a corresponding piston pin for varying piston height, also utilize hydraulic control systems for operating an internal combustion engine in various compression ratio modes.
Accordingly, the inventor herein has recognized the need to provide an improved variable compression engine having a connecting rod that can be quickly and reliably operated without utilizing a hydraulic control system.
An internal combustion engine is provided having a variable compression ratio apparatus, a field-sensitive fluid coupled to the variable compression ratio apparatus, and a circuit for applying a field to the field-sensitive fluid to configure the variable compression ratio apparatus in accordance with a selected compression ratio of the internal combustion engine. Preferably, the field-sensitive fluid is a magnetorheological (MR) or electrorheological (ER) fluid.
In accordance with a preferred embodiment of the present invention, the engine includes an apparatus for selectively varying a compression ratio of an internal combustion engine, the apparatus having a bearing retainer disposed between a connecting rod and a crankpin of the engine, and wherein the bearing retainer includes an inner portion in communication with the crankpin and an outer portion in communication with the connecting rod such that the connecting rod is axially movable relative to the bearing retainer along a longitudinal axis of the connecting rod. A field-sensitive fluid is provided within the connecting rod for communicating with the bearing retainer so as to vary the effective length of the connecting rod. A circuit, which may for example include an electromagnet, is further provided for applying a field to the fluid so as to maintain the connecting rod at a position relative to the position of the bearing retainer. When commanded, the effective length of the connecting rod at top-dead-center is thus controllable in accordance with a desired compression ratio mode of the internal combustion engine. A reciprocating internal combustion engine is also provided having the above-described compression ratio apparatus.
An advantage of the above-described variable compression ratio apparatus is that transitions between two or more compression ratio modes can be accomplished quickly and reliably without requiring the rotation of an eccentric ring member, and without requiring the use of a complex and costly hydraulic control system. By using the inertial forces acting on the rod to vary the rod""s effective length, and by using the field-sensitive fluid together with an applied magnetic or electric field to xe2x80x9clockxe2x80x9d and xe2x80x9cunlockxe2x80x9d the rod length, transitions between compression ratio modes can be performed within a single engine cycle without reliance on a hydraulic control system.
In a related aspect of the present invention, a corresponding system is also provided having the above-described variable compression ratio apparatus. In accordance with a preferred embodiment, the system further includes at least one sensor for measuring an operating condition of the internal combustion engine, and an engine controller coupled to the internal combustion engine, the sensor and the variable compression ratio apparatus for generating, based on the measured operating condition of the internal combustion engine, a control signal required to configure the variable compression ratio apparatus in accordance with the desired compression ratio of the internal combustion engine.
A related method is also provided, the method including the steps of: measuring at least one operating condition of the internal combustion engine; axially moving the connecting rod relative to a corresponding bearing retainer along a longitudinal axis of the connecting rod, wherein the position corresponds to a selected compression ratio of the internal combustion engine, and wherein the bearing retainer is in communication with a field-sensitive fluid disposed within the connecting rod; and applying a field to the field-sensitive fluid to maintain the connecting rod at the position corresponding to the selected compression ratio.
Further advantages, objects and features of the invention will become apparent from the following detailed description of the invention taken in conjunction with the accompanying figures showing illustrative embodiments of the invention.